Abstract
AbstractMicroplastics (MPs) are small, plastic particles of various shapes, sizes and polymers. Although well studied in marine systems, their roles and importance in freshwater environments remain uncertain. Nevertheless, the restricted ranges and variable traits of freshwater fishes result in their communities being important receptors and strong bioindicators of MP pollution. Here, the current knowledge on MPs in freshwater fishes is synthesized, along with the development of recommendations for future research and sample processing. MPs are commonly ingested and passively taken up by numerous freshwater fishes, with ingestion patterns often related to individual traits (e.g. body size, trophic level) and environmental factors (e.g. local urbanization, habitat features). Controlled MP exposure studies highlight various effects on fish physiology, biochemistry and behaviour that are often complex, unpredictable, species‐specific and nonlinear in respect of dose–response relationships. Egestion is typically rapid and effective, although particles of a particular shape and/or size may remain, or translocate across the intestinal wall to other organs via the blood. Regarding future studies, there is a need to understand the interactions of MP pollution with other anthropogenic stressors (e.g. warming, eutrophication), with a concomitant requirement to increase the complexity of studies to enable impact assessment at population, community and ecosystem levels, and to determine whether there are consequences for processes, such as parasite transmission, where MPs could vector parasites or increase infection susceptibility. This knowledge will determine the extent to which MP pollution can be considered a major anthropogenic stressor of freshwaters in this era of global environmental change.
Highlights
Freshwater fish MP exposure levels have been highly variable, based on the type, size and shape of MPs, and, taking weight alone, span at least five orders of magnitude from 10 μg/L (Qiao et al, 2019) up to 6 g/L (LaPlaca & van den Hurk, 2020)
Microplastics exposure studies have revealed a wide range of effects in freshwater fishes (Table 2), but there remains considerable uncertainty in how these translate into measurable impacts in wild populations, above the individual level (Figure 2)
Studies highlight considerable variability in ingestion patterns and effects, but that these differences can generally be explained through a combination of traits of the fish, its environment and the MP characteristics
Summary
Freshwater fish MP exposure levels have been highly variable, based on the type, size and shape of MPs, and, taking weight alone, span at least five orders of magnitude from 10 μg/L (Qiao et al, 2019) up to 6 g/L (LaPlaca & van den Hurk, 2020). GIT oxidative stress and histological damage are common impacts at the organ/tissue level (Figure 2), where the processing of MPs and/or any associated chemicals induce immune response, resulting in localized cell damage and altered morphology of physiological structures (Lu et al, 2016; Yu et al, 2020).
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